Immunology Flashcards
Define immunology
The study of the physiological mechanisms that we use to defend our bodies against invasion by other organism
Hypervariable regions
Antibodies have 3 and these determine the complementary fit between the antigen and the antigen binding site of the antibody
CDR’s
Complementary determining regions (part of the antibody and align with the loops at the end of the variable domain) which interact with the antigen and give the antibody specificity
Antigen binding
Bind to the antigen binding site of the antibody by non covalent forces (hydrogen, ionic, VDWs and hydrophobic)=weak bonds so a large number is required to ensure the 2 parts bind together
Antibody affinity
Strength of the total non-covalent interactions with a single antigen binding site on the antibody and a single epitope on the antigen
Antibody avidity
Overall strength of multiple interactions between an antibody with multiple antigen binding sites and a complex antigen with multiple epitopes
Antibody cross-reactivity
Antibody with an antigen binding site complementary to a specific antigen can also recognise different antigens with a similar structure
IgG
- Gamma heavy chain
- Must abundant immunoglobulin
- Found in the blood and extracellular fluid
- Variability of the heavy chain at the hinge region gives rise to 4 different subclasses which have subtly different functions
- Activates the classical complement pathway
- Can be actively transported across the placenta to give the foetus passive immunity and therefore protect it
IgA
- alpha heavy chain
- Variation of the heavy chain at the hinge region gives rise to 2 different subclasses which have subtly different functions
- found in breast milk
- multimeric due to formation of J chains, but IgA in the blood is monomeric
- monomer in the blood and dimer in secretion
- Secretion protects mucosal surfaces
- Secretory component of antibody protects it from degradation
IgM
- mu heavy chain
- first immunoglobulin synthesised from infection in the primary immune response
- 5 monomers joined and held together by J chains=multimeric
- activates agglutination and the complement pathway
- multiple binding sites allow for agglutination and to compensate for the low affinity
- mainly found in the blood
IgE
- epsilon heavy chain
- produced to defend against parasitic infections and allergic reactions
- binds to the high affinity Fc receptors on the mast cells and basophils which are complementary to this specific antibody
- the cross linking by antigen triggers the mast cell activation, degranulation and hence histamine and other inflammatory mediator release
- found at low concentrations/levels within the blood serum
IgD
- sigma heavy chain
- very low blood serum concentration
- Involved in the B cell development and activation
Light chains
Can be either both kappa or both lambda (cannot be one of each because the antibody molecule is symmetrical)
Antibody roles
Roles in medicine, laboratory science and in defence
Laboratory science antibody roles
vast range of diagnostic and research applications
Medicine antibody roles
- Monoclonal antibody therapy for cancer treatment
- Antibody levels can help diagnose disease and monitor disease progress
- Pooled antibodies for passive immunity/therapy
Defence antibody roles
- Neutralisation of toxins by antibodies binding to antigens/toxin molecules
- Passive immunity in newborns with the antibodies gained from the mother
- Opsonisation=coating of the pathogens with antibodies (proteins) to promote phagocytosis, aiding the phagocytes
- Agglutination=antibodies can clump the pathogens together due to their multiple antigen binding sites
- Complement activation via the classical pathway
Where are the B cells produced and mature?
Produced by haematopoietic stem cells in the bone marrow and mature here also before being released into the bloodstream/circulation as naïve B lymphocytes
Role of B lymphocytes
Occur in humoral immunity and if complementary antigen to binding site is encountered, cell proliferation occurs by clonal selection and antibodies of the same specificity will be synthesised
Antigen epitope
The specific part of the antigen to which the receptor binds. Antigens have multiple epitopes so a single antigen can be targeted by multiple antibodies
B cell receptor
Membrane bound antibody which binds to the epitope of antigens. Also consists of a di-sulfate linked heterodimer with an IgA and IgB component
Di-sulfate linked heterodimer
Cytoplasmic tail is long enough to interact with the intracellular components and trigger a cascade
Immunoglobulin gene rearrangement
- Accounts for multiple B cell receptors
- Occurs in bone marrow when progenitor B cells are converted to mature B cells
- Immature B cells begin with germline DNA
- Heavy chain has 3 gene segments=V,D and J regions
- Regions are composed of many segments and a singular segment is selected from each region to join to the constant region
- VDJ regions formed from recombination with addition/removal of DNA, then transcription and splicing
- light chain is V and J=no D
- 3 enzymes involved=kappa, lambda, all heavy